34 2 



NORTH AMERICAN INDEX FOSSILS. 



384. S. texta (Hall). (Figs. 436-437. 



Mississippic. 



La 



rge, 



to 



as long as broad. Height often greater than 

 length. Hinge line forming the greatest width of the shell. 

 Pedicle valve the more convex, very prominent at umbo; mesial 



sinus deep, rapidly increasing in 

 width from beak to front where it 

 occupies about one fourth of the 

 anterior margin ; beak angular ; 

 cardinal area high and nearly 

 straight. Brachial valve most 

 convex near the front. Surface 

 marked by about 20 simple plica- 

 tions on each side the median line, 

 crossed by concentric growth 

 lines. Much heavier, wider and 

 more robust than S. carter! . 



Waverly-Keokuk of Kentucky, 



Fig. 437. Syringothyris texta, var. 

 Xf (Ohio Pal.). 



Indiana, Ohio, Iowa, Illinois. 



CVII. Amboccelia Hall. 



Small. Spnfer-hke. Pedicle valve greatly elevated, with a 

 conspicuous, strongly incurved umbo ; cardinal area arched and 

 delthyrium open. Brachial valve with long, narrow cardinal 

 process, crural plates long, parallel, 

 erect; four well defined adductor 

 scars present near the anterior mar- 

 gin. Devonic-Carbonic. 



385. A. praeumbona Hall. (Fig. 



438, a-b.) Devonic. 



Hinge line less than the great- 

 est width of shell, with rounded 

 cardinal extremities. Pedicle valve 

 very ventricose, bearing a shallow 

 impressed median line. Brachial 

 valve slightly convex. Surface 

 marked only by concentric striae 

 which are sometimes crowded into imbricating folds. 



Hamilton of New York. 



Fig. 438. a-b, Amboccclia prceum- 

 bona ; c-d, Amboccelia umbonata (Pal 

 N. Y. IV. ). 



